Mixer - Can invert the spinning direction cause serious trouble? 2

[guerky]

I have a reactor with a botton valve suffering with obstruction several times a week, thanks to some heavy solids in suspension depositing over it (excess of one reagent).
The mixer is a pitched turbine with four paddles that aparently forces the bulk of the mixture towards the bottom in the actual spinning direction.
I wish to invert this spinning direction, hoping to keep most of this solid particles in suspension by favoring an upwards axial flow. The reaction is very fast, and the mixing is actualy good. Also, there is no risk of unwanted parallel reactions.

Can this work?
Can i expect some heavy loss in agitation quality or in the worst case scenario i will have just an increased energy consumption?
I also thank for any hints, rules of thumb or materials on mixing issues.

 

[guerky]

itdepends,

Its a simple acid-base reaction prepared to cut some on the main reactors, but the solvent isnt water, its DMSO. The media becomes dense (1,3 kg/m³) and viscous (100cP+), especially if the heating is suspended and the mixture chill below 50°C (a common mistake, since the temperature rising above 100°C with KOH adition disable the heating loop, requiring manual override for security reasons).

Update: i found that some batches of KOH have scales about two times larger and thicker than the others. That explain why the plugging doesnt happens in every batch (batches with these KOH represents 90% of the pluging cases). Saddly, i still have this thing on deposit for two full production months, and a new shipment arriving on january.

Changing the paddles would take about two days for decontamination and confined space work protocols. This is scheduled for 12/27. For now, i've installed a 1/2" 1,5 kgf/cm² nitrogen line for bubbling the botton during the KOH load.
my guess is that decreasing the aparent density of the media with gas boubbles would increase the speed and shear on that region (yes, i love quickfixes). Seens to be working fine, but plugging still happen from time to time.

There is an advantage in using a propeller instead of an impeller? I mean, the mixing itself tends to be better with propeller, but impellers like marine paddles would not have an edge over propellers like a pitched blade turbines when coming to keep solids in suspension? As mentioned on above posts, i'm willing to sacrifice shear for axial flow, since most of the solids are readily soluble before saturation.

 

[Latexman]

I have seen cases where a small "tickler turbine" added under the shaft and steady bearing to provide mixing in the area under the shaft. Maybe, that's an option now or later if the propeller isn't a 100% solution.

Good luck,
Latexman

To a ChE, the glass is always full - 1/2 air and 1/2 water.

 

[gerhardl]

guerky,

If you see a positive reaction with adding gas bubbles, it could perhaps be interesting for you to have a further look into details.

Suggestions for check:
-Would it be easier, cheaper and possible to use air instead of nitrogen?
- With a correct balanced pressure and amount of gas you could experiment with a length of gas-dispersing holes in a pipe or host to add to the turbulence and direction/position of the gas outlet.

 

[guerky]

gerhardl,

Using air is out of question. DMSO is a very dangerous solvent (underestimated because of its widespread utilization), and we already experienced some frightening "almost-runaways" reactions with it at mild conditions.

About the holes, i'll check it out. Thanks.